I. Field of the Invention
The present invention relates to elevator systems and, more particularly, to linear motor driven elevator systems.
II. Description of Related Art
Linear motor driven elevator systems are known. See, for example, U.S. Pat. Nos.: 4,402,386; 5,005,672; 5,033,588; 5,062,501 and 5,074,384. Such systems include a plurality of walls forming a hoistway associated with a number of substantially vertical guide rails on which are slidably mounted an elevator car and a counterweight assembly. The counterweight assembly includes a primary element of a linear motor and counterweights, all suitably mounted within a movable frame. A secondary element of the linear motor is located within the interior of the hoistway. The secondary extends a vertical distance (i.e., has a height dimension) substantially equal to a maximum height of the hoistway. A roping arrangement mechanically connects the car to the counterweight assembly so that a total travel distance of the car in one direction equals a total travel distance of the counterweight assembly in an opposite direction. The primary receives electrical energy from an AC source through a traveling power cable and interacts electromagnetically with the secondary to move the counter-weight assembly in vertical (up and down) directions along the guide rails.
U.S. Pat. No. 4,570,753 teaches a linear motor elevator having a stationary primary affixed to a hoistway wall and also having a flexible secondary affixed to a counterweight assembly. A total travel distance of the car equals a total travel distance of the secondary.
In order to use building space efficiently and economically, elevator system designers strive to reduce the volume within the interior of the hoistway required by the elevator system. U.S. Pat. No. 5,036,954 teaches a traction elevator system having hybrid roping in which a car roping ratio is less than a counterweight assembly roping ratio. Thus, the distance traveled by the counterweight assembly is shorter than the distance traveled by the elevator car during normal operation of the elevator system. The volume within the interior of the hoistway required by the counterweight assembly during normal operation of the traction elevator system is reduced.
The known systems have proven to be not entirely satisfactory because they continue to occupy a large volume of building space. The present inventors have achieved reductions in the volume occupied by a linear motor elevator system.